I have stood at more Indian kitchen counters than I can count, chopping onions for the tadka, eyes streaming, while someone inevitably tells me to hold a matchstick in my teeth or chew gum. Some of those tricks actually work, and there’s real chemistry behind why onions make us cry in the first place – once you understand it, stopping it gets a lot easier.
Why Do Onions Make You Cry?
Onions store sulphur compounds in their cells, and when you cut into one, you rupture those cells and release an enzyme that reacts with the sulphur compounds to form a volatile gas called syn-propanethial-S-oxide. That gas rises up and reaches your eyes, where it reacts with the moisture on their surface to form a mild sulphuric acid, which is what triggers your eyes to water and sting. It’s not the onion trying to punish you – it’s a very effective defence mechanism the plant evolved to deter animals from eating it.
Where This Fits Into Everyday Indian Cooking
Onions are the base of an enormous number of Indian dishes, from the humble tadka to rich gravies, which means most home cooks are chopping them daily. Because of how central onions are to Indian food, generations of kitchen wisdom have built up around avoiding the tears – some of it genuinely useful science, some of it more superstition than substance.
The Real Science-Backed Fixes
- Chill the onion in the fridge for 30 minutes before cutting; cold slows down the enzyme reaction that releases the irritating gas
- Cut onions near a running exhaust fan or open window, so the gas disperses before it reaches your eyes
- Use a sharp knife rather than a blunt one; a clean cut crushes fewer cells and releases less gas
- Cut off the root end last, since it contains the highest concentration of the sulphur-releasing enzyme
- Wearing glasses, swim goggles or contact lenses creates a physical barrier that keeps the gas away from your eyes
Tips
- Soaking peeled onions in cold water for 10-15 minutes before chopping reduces the sulphur compounds on the surface
- Cutting onions under a light stream of running water helps wash the gas away, though it makes handling the knife trickier
- Chewing gum or breathing through your mouth while cutting can help, since it reduces how much gas reaches your nasal passages
- Old tricks like holding a matchstick in your teeth are mostly anecdotal, but the cold-onion and sharp-knife methods are backed by the actual chemistry
Next time your eyes start stinging over the chopping board, you’ll at least know exactly what’s happening at a chemical level – and which of the kitchen tricks are actually worth using. A cold onion and a sharp knife will get you further than any old wives’ tale.